The following U.S. patents, all assigned to the assignee hereof, are hereby incorporated by reference for their teachings relating to the structure and operation of full-color photosensitive devices such as used in office equipment and digital cameras: U.S. Pat. Nos. 5,148,268 and 5,543,838.
The present invention relates to color photosensitive devices, such as used in image input scanners and digital cameras, wherein light from an image received by the device is converted to a set of image signals.
Monochrome image sensor arrays typically comprise a linear array of photosensors which raster scan an image bearing document and convert the reflected light from each microscopic image area viewed by each photosensor over time to image signal charges. Following an integration period, the image signals are amplified and transferred to a common output line or bus through successively actuating multiplexing transistors.
In a well-known design of a photosensitive device such as used in an image input scanner, separate linear arrays of photosensors are arranged in parallel on a single sensor bar, and caused to move in a scan direction relative to the original image generally perpendicular to the direction of the arrays. The photosensors in each array are provided with a filter thereon of one primary color. As the sensor bar including the three rows of photosensors moves along the original image, each portion of the area of the original image is exposed to each of the rows of photosensors. As each filtered row of photosensors moves past each particular area in the original image, signals according to the different primary color separations of that area are output by the particular photosensors in each row. In this way, three separate sets of signals, each relating to one primary color, will be produced by the linear arrays of photosensors.
In the general art of imaging, including the art of television and photographic film, it is known that the color-sensitive photoreceptors in the human eye tend to have gaussian responses which peak respectively at approximately in the blue, green, and orange parts of the spectrum, as opposed to the blue, green, and red parts to which electronic devices are typically sensitive. It would thus be desirable to have an imaging apparatus or film with a responsivity which xe2x80x9cpeaksxe2x80x9d at orange (about 600 nm) rather than red (about 550 nm). Achieving this orange sensitivity has proven to be difficult. Light-transmissive filters which have a gaussian peak of admitting light at 600 nm exist, but tend to be difficult or expensive to manufacture.
The present invention is directed to techniques for designing a photosensitive imaging device wherein at least one set of photosensors is particularly sensitive (that is, has a response that substantially peaks) in the orange (approximately 600 nm) part of the visible spectrum.
U.S. Pat. Nos. 5,148,268 and 5,543,838, incorporated by reference above, disclose circuit designs for color image sensor arrays for recording full-color original images as digital data.
U.S. Pat. No. 4,870,496 discloses a video camera in which a yellow-orange filter and an infrared filter are used in combination; however, the reference does not disclose isolating the orange portion of the visible spectrum.
U.S. Pat. No. 5,914,749 discloses a color imaging device in which individual photosensors in an array are filtered to receive magenta, white, or yellow portions of the visible spectrum. The outputs from the various types of photosensors are subjected to mathematical algorithms to infer other primary colors in the image being recorded.
U.S. Pat. No. 6,201,293 is cited as a teaching of the general technique of placing light-transmissive filters over various photosensors in a silicon chip.
PCT Patent Application WO 91/13942 discloses a material suitable for an orange band-pass optical filter.
According to one aspect of the present invention, there is provided an imaging apparatus, comprising a first set of photosensors, for recording light of a substantially red wavelength and longer wavelengths, and a second set of photosensors, for recording light of a substantially infrared wavelength and longer wavelengths. Means are provided for subtracting signals from the second set of photosensors from signals from the first set of photosensors, thereby yielding difference signals substantially related to light of substantially orange wavelengths.
According to another aspect of the present invention, there is provided an imaging apparatus, comprising a first set of photosensors, having associated therewith a light-transmissive filter for admitting light of a substantially orange wavelength and longer wavelengths. The first set of photosensors has an epitaxial layer configured to have a decreasing response with increasing wavelengths of incident light over 600 nm.
According to another aspect of the present invention, there is provided an imaging apparatus, comprising a first set of photosensors, a first light-transmissive filter for admitting light of orange and longer wavelengths to the first set of photosensors and an infrared filter for blocking light of a substantially orange wavelength and higher wavelengths to the first set of photosensors.
According to another aspect of the present invention, there is provided an imaging apparatus, comprising a first set of photosensors, a first light-transmissive filter for admitting light of a substantially orange wavelength and longer wavelengths to the first set of photosensors, and a light source, for emitting light which is reflected by an image to be recorded. The light source has an emission spectrum which is attenuated in the infrared range.